1. Field of the Invention
The present invention relates to reversible, electrically controllable, light transmission (RECLT) films, articles of manufacture, compositions and processes for their manufacture. Electrochromic, reversible metal electrodeposition, liquid crystal, and dispersed particle systems display comprise some RECLT phenomena.
Electrochromic materials change color upon the application of an electrical current to induce an electrochemical reaction in the material. Unlike reversible metal electrodeposition compositions and processes for light modulation, electrochromic processes do not require electrodeposition to produce a light modulating effect. Reversible metal electrodeposition for light modulation relies on the deposition and removal of a metal from a substrate to control the transmission of light. By contrast, liquid crystal systems switch between transmissive and opaque light scattering states upon the application of an electric currents, but require substantial voltages to maintain transparency.
Electrochromic devices comprise an electrochromic film operatively associated with a substantially transparent electrode and a counter electrode. The electrochromic film generally is sandwiched between the transparent electrode and the counter electrode and will change color on the application of an electric current. Reversing the polarity of the current will cause the film to lose color.
In operation, reversible metal electrode position for light modulation involves applying a negative electric potential to a first electrode, relative to a second electrode. The applied potential tends to cause deposited metal to dissolve from a second electrode in an electrolytic solution in between the two electrodes followed by electrodeposition from the solution onto the first electrode. This impedes the propagation of radiation through the device. Upon reversing polarity, and applying a positive electrical potential to the first electrode relative to the second electrode, deposited metal dissolves from the first electrode and onto the second electrode to increase the light transmissivity of the device.
The active layer of a dispersed particle system has needle shaped particles suspended in an organic fluid or gel. The dispersed particle device comprises the organic fluid or gel placed between two electrical conductors. Applying an electrical field causes the particles to align causing transmission to increase. Turning the field off, causes the particles to align randomly and become light absorbing.
As noted, liquid crystal-based systems switch between transmissive and opaque scattering states upon the application of an electric current and reversal of the polarity of the electric current. The liquid crystal device comprises a liquid crystal material well known in the art, combined with a matrix material sandwiched between transparent positive and negative electrodes.
2. Related Art
Many related art electrochromic elements employ tungsten oxide since it changes from a clear, transparent state to a colored state upon the application of an electric current. Transition metal compounds such as transition metal oxides also display electrochromic properties when changing from one valence state to another such as transition metals varying between the +2 and +3 valence state or transition metals varying between the +3 and +4 valence states. The related art also describes many organic compounds that display electrochromic properties.
Color changes, rates and performance characteristics, whether inorganic or organic electrochromic materials, depend on the electrochromic material used as well as the entire electrochromic system including the electrolyte and cell configuration. P. N. Moskalev I. S. Kirin, Opt. Spectrosc., 29, 220 (1970), and P. N. Moskalev and I. S. Kirin, Russ. J. Phys. Chem., 47, 1019 (1972) describe electrochromic reactions of rare earth diphthalocyanines. Similarly, M. M. Nicholson and F. A. Pizzarello, J. Electrochem Soc., 127, 2490 (1979) describe color changes in a lutetium diphthalocyanine film on tin oxide in an aqueous electrolyte of potassium chloride or sodium sulfate. M. M. Nicholson and F. A. Pizzarello, J. Electrochem Soc., 128,1740 (1981) amplify their earlier work. D. Lawton, B. Ely and G. Elliott, J. Electrochem. Soc., 128, 2479 (1981) describe electrochromic action of other rare earth diphthalocyanines and find changes similar to lutetium and ytterbium diphthalocyanines in a variety of aqueous and organic electrolyte liquids.
Viologens, i.e., 4,4xe2x80x2-dipyridinium compounds, also display electrochromic properties in aqueous and organic liquid electrolyte systems. R. J. Jasinski, J. Electrochem. Soc., 124, 637 (1977) describes the electrochromic properties of n-heptylviologen in salt solutions and their dependence upon specific anions, cations and metals present. H. T. van Dam and J. J. Poujee, J. Electrochem. Soc., 121, 1555 (1974) developed data on the differences in redox potentials between ethylviologen and benzylviologen in aqueous and/or liquid solvents. J. Bruinink and C. G. A. Kregting, J. Electrochem. Soc., 125, 1397 (1978) discuss the electrochromic changes of diheptylviologen films on tin oxide electrodes in an aqueous electrolyte. B. Reichman, F. F. Fan and A. J. Bard, J. Electrochem. Soc., 127, 333 (1980) investigated the photoreduction of aqueous solutions of heptylviologen bromide on p-gallium arsenide in photoelectrochemical cells. H. T. van Dam, J. Electrochem. Soc., 123, 1181 (1976) sets out the differing conductants of heptylviologen in aqueous and organic solvents. C. J. Schoot et al., Applied Physics, Vol. 23, No. 2 (Jul. 15, 1973) pp. 64-65 describes other organic electrochromic materials in combination with liquid electrolytes. L. G. van Uitert et al., Applied Physics Letters, Vol. 36, No.1 (Jan. 1, 1980) pp. 109-11 discloses anthraquinone red electrochromic display cells.
Sammells, U.S. Pat. Nos. 4,750,817 and 4,807,977 describe multicolor electrochromic flat-panel displays based on solid-state electrochromic cells with solid polymer electrolytes. The references disclosed the use of polyvinylidene fluoride as an alkali ion conducting polymer in combination with various electrochromic compounds and an electrolyte.
Hirai, U.S. Pat. No. 4,550,982 illustrates an electrochromic display device based on a polymer layer containing at least one organic electrochromic material and at least one anionic material to provide a polymer redox layer. Examples of polymer materials include fluororesins such as polyvinylidene fluoride.
Eid et al., U.S. Pat. No. 5,332,530 describe a device for the modulation of light consisting of two glass substrates, each coated with a transparent electrically conducting layer such as tin oxide or a mixture of indium oxide and tin oxide (ITO). The substrates have a thin layer of an electrolyte containing metal ions sandwiched in between them. The application of an electric current to the electrodes results in the deposition of the metal on one of the substrates by means of an electrochemical reduction. Reversing the current causes the metal to redeposit as an ionic species in the electrolyte.
The related art devices according to Eid et al. relied on an aqueous electrolyte containing a strong mineral acid to prevent hydrolysis of metal salts in the electrolyte. The electrolyte had a low pH and consequently the drawback of generating hydrogen gas concurrently with electrodeposition of the metal layer. Additionally in some instances this caused the degradation of the transparent electrically conductive material. Eid et al. addressed the problem by employing a polymeric electrolyte dissolved in an organic solvent to produce a gel-like matrix. Eid et al. disclose a commercial grade of polyvinylidene fluoride as one of the polymeric electrolytes.
Tench et al., U.S. Pat. No. 5,903,382 also employed a polymeric material in an electrolytic composition used for reversible metal electrodeposition in a light modulating device. Tench et al. describe this as a xe2x80x9csolid statexe2x80x9d gel electrolyte and the polymer as electrochemically inert, selected to minimize sensitivity to atmospheric contamination. Typical polymers comprise acrylic materials such as polymethyl methacrylate or polyacrylonitrile.
Although various references disclose the use of polyvinylidene fluoride resins in the manufacture of RECLT devices, commercial grades of these resins do not have the low solubility, high thermal stability and strength, or optical clarity required for the production of a high quality RECLT device, especially an electrochromic device.
Accordingly, an RECLT film, article of manufacture or composition avoiding the difficulties encountered with polyvinylidene fluoride having high solubility, low thermal stability and strength, and low optical clarity would provide an advantage over polyvinylidene fluoride materials presently used, which slow down the speed of the cell and do not provide sharp differences between the activated and inactivated configurations of the cell.
The present invention avoids these and other difficulties encountered in the prior art by providing an RECLT film, process of manufacture, article of manufacture and composition based on a polyvinylidene fluoride copolymer having exceptionally low solubility and high thermal stability and strength, and high optical clarity that substantially obviates one or more of the foregoing and other problems due to the limitations and disadvantages of the related art.
The written description that follows sets out additional features and advantages of the invention and makes them apparent, and which the skilled artisan can also learn by practice of the invention. The RECLT film, process of manufacture, article of manufacture and composition of the invention as particularly pointed out in the written description and claims hereof as well as the appended drawings illustrate how to obtain the objectives and other advantages of the invention.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described, the invention comprises an RECLT, film, process of manufacture, article of manufacture, and composition based on a narrow composition distribution (NCD) polyvinylidene fluoride copolymer, an electrolyte and known organic or inorganic RECLT materials.